The invention relates to a liquid sample analyzer, and more particularly, to such apparatus which analyzes a liquid sample through light absorbance or ion electrode process.
The concentration of liquid sample, such as blood, is automatically determined and analyzed by using a light absorbance analyzer or ion electrode analyzer. A conventional arrangement of light absorbance analyzer is illustrated in FIG. 1. Referring to FIG. 1, light from a light source 1 is split in two directions, one being passed through an optical filter 2a to produce monochromatic light, which is transmitted through a collimator lens 3a into a colorimetric cell 8b. Light passing through the cell 8b impinges on a light receiving element 4a, which converts the light output into an electrical signal, which is in turn supplied to one input terminal 5a of an operational amplifier 5 as a sample signal. The remaining portion of the light from the source 1 is passed through another optical filter 2b to produce monochromatic light, which is then passed through a collimator lens 3b to impinge on another light receiving element 4b as a reference light. In response to the light input, the element 4b produces an electrical reference signal, which is supplied to the other input terminal 5b of the amplifier 5. The amplifier 5 effects a comparison of the sample signal and the reference signal, and the analyzer output is recorded by a recorder 6.
The cell 8b is formed as part of a colorimeter tube 8 which comprises a transparent piping. The colorimeter tube 8 is centrally formed with a U-bend 8a, the right-hand limb of which is shaped as a T-section which includes a sample supply portion 8c and an air bubble remover 8d, and the left-hand limb of which communicates with the colorimetric cell 8b which extends horizontally and which is in turn in communication with a vertically extending liquid drain 8e. A sample is contained within the cell 8b and the collimated light from the lens 3a is passed therethrough. Sample 7, such as blood, which is supplied to the colorimetric tube 8 is fed through the supply portion 8c while it is partitioned by air bubbles 9. However, immediately before the sample 7 enters the U-bend 8a, it is automatically debubbled by the remover 8d which has an open top. Subsequently, the sample 7 flows into the cell 8b where its concentration is determined with transmitting light, and is finally disposed of through the drain 8e.
A major problem with the arrangement described above is a contamination of the cell 8b, which results in a degradation in the accuracy of analysis. Such contamination may be prevented by flushing an old sample off the wall of the cell with an increased flow of new sample 7. Alternatively, an aqueous standard solution may be passed through the cell between the measurement of successive samples, thus flushing away an old sample which remains attached to the wall of the cell. However, such techniques disadvantageously require the use of a waste solution in large quantities. In addition, as will be noted from FIG. 1, the closed construction of the colorimetric cell 8b makes it difficult to remove any bubble 9 which might have made its way into the cell 8b, resulting in noises which appear in the result of determination.
FIG. 2 shows an exemplary arrangement of conventional analyzer which utilizes the ion electrode technique. As shown, an ion concentration detector comprises a glass tube 11 through which a quantity of liquid sample 12 is supplied, an ion electrode 13 which is connected in communication with the glass tube 11 by means of connecting tube 14 and including a sample passage tube 15, a support tube 21 which is connected in communication with the tube 15 by means of connecting tube 20, and a double junction reference electrode 19 mounted on the support tube 21 and having its lower end disposed in contact with sample 12 contained within the tube 21. In the example shown, the ion electrode 13 is formed as a glass electrode for detecting Na ions, and comprises sample passage tube 15 formed of Na ion-sensitive glass film such as Li-Al-Si, An-Al-Si or similar composition, AgCl electrode 16 coiled around the tube 15, an outer tube 17 which contains the electrode 16 and the tube 15, and a filling of internal standard solution 18 contained in the tube 17.
The reference electrode 19 comprises an outer tube 23, a porous member 22 secured to its lower end for contact with liquid sample 12 and having a port 23a formed in its sidewall for replenishing a reference solution 27, an inner tube 25 disposed within the outer tube 23 and having a porous member 24 secured in its lower end for contact with the reference solution 27 contained within the outer tube 23 and having a port 25a formed in its sidewall and extending through the outer tube for replenishing reference solution, AgCl electrode 26 disposed within the inner tube 25, a quantity of external reference solution 27 which fills the outer tube 23, a quantity of internal reference solution 28 which fills the inner tube 25, and a cap 29 to which the tubes 23, 25 and electrode 26 are secured together. The electrode 26 is in electrical contact with liquid sample 12 through reference solution 28, porous member 24, reference solution 27 and porous member 22.
The ion electrode 13 and reference electrode 19 are connected to input terminals 30a, 30b, respectively, of an amplifier 30, the output terminal 30c of which is connected with an indicator 31. The Na ion concentration in the liquid sample 12 is determined as a potential difference across the ion electrode 13 and the reference electrode 19 which is proportional to the logarithm of Na ion concentration. The potential difference is amplified by the amplifier 30 and is displayed by the indicator 31.
In the arrangement of FIG. 2, a contamination of sample passage tube 15 and porous member 22 again poses a problem, causing a degradation in the accuracy of analysis. The prior art practice to avoid this has been to flush away an old sample with an increased quantity of sample 12, again resulting in a wasteful use of sample solution, in particular when the liquid sample is blood.